A new analysis says water rates in San Diego must go up another 44.2% between 2028 and 2031 even though the City Council agreed in October to raise them a cumulative 31.3% this year and next. If the council ends up approving additional hikes that large when they come to a vote next year, the cumulative six-year rate increase would amount to more than 90%. The 54-page analysis, which was presented to the council Monday, also says sewer rates must rise a total of 15% in 2030 and 2031. … Council members and other city leaders vowed Monday to spend the next 12 to 18 months searching for ways to boost revenue or cut spending for the city’s water and sewer systems that could prevent such large hikes.